Cyanine dye containing a tetrahydrobenzothiazole nucleus



Patented Bee. 14, 1943 LINETED STATES PATENT QFFICE CYANINE DYECONTAINING A TETRAHY- DROBENZOTHIAZOLE NUCLEUS Jersey No Drawing.Application November 9, 1939, Serial No. 303,618

4 Claims.

This invention relates to cyanine dyes containing atetrahydrobenzothiazole nucleus and to a process for preparing suchdyes.

Cyanine dyes contain at least two auxochromic nitrogen atoms, the oneternary and the other quaternary, the one nitrogen atom lying in oneheterocyclic nucleus and the other lying in another heterocyclicnucleus, the two nitrogen atoms being connected by a conjugated carbonchain. A number of cyanine dyes containing benzothiazole nuclei as oneor both of the aforesaid heterocyclic nuclei are known.

We have now found that it is possible to prepare cyanine dyes in whichone or both of the aforesaid auxochromic nitrogen atoms lie in a4,5,6,7-tetrahydrobenzothiazole nucleus. We have further found thatthese new cyanine dyes sensitize photographic emulsions strongly andcleanly, i. e. without producing excessive fog.

It is, accordingly, an object of our invention to provide new cyaninedyes. A further object is to provide a method for preparing such dyes. Afurther object is to provide photographic emulsions sensitized with suchdyes. Other objects will appear hereinafter.

As starting material for the preparation of our new dyes, we employ.2-alkyl-4,5,6,'7-tetrahydrobenzothiazoles, particularly2-methyl-4,5,6,7- tetrahydrobenzothiazole. We first convert thesetetrahydrobenzothiazole bases to quaternary salts by reacting the baseswith esters, such as alkyl halides, alkyl sulfates .oralkyl-p-toluenesulfonates, for example.

To prepare pseudocyanine dyes from such quaternary salts, we react thequaternary salts with 2-halogenoquinoline quaternary salts, in thepresence of an acid-binding a ent, such, for example, as sodiumethylate, sodium carbonate, pyridine or a strong tertiary organic base(e. g. trimethylamine, triethylamine and N-methylpioeridine). Strongorganic bases are those which have a dissociation constant substantiallygreater than that of p ridine. We have found it advantageous to employstrong tertiary organic bases.

Instead of 2-halogenoquinoline quaternary salts, we can employ2-alkylmercaptoor 2-arylmercaptoquinoline quaternary salts to condensewith the quaternary salts of 2-alkyltetrahydrobenzothiazoles, in thepresence of an acid-binding agent. Z-alkylmercaptoand2-arylmercaptoquinoline quaternary salts are described in United StatesPatent 2,117,986, dated May 1'7, 1938.

Using Z-halogenopyridine or Z-halogenopyridine quaternary salts insteadof 2-halogenoquinoline quaternary salts, We can preparepyridopseudocyanine dyes containing a tetrahydrobenzothiazole nucleus.

Using Z-alkylmercaptoor 2-arylmercaptobenzothiazole quaternary saltsinstead of Z-halogenoquinoline quaternary salts, we can prepare simplecyanine dyes other than pseudocyanine dyes.

To prepare symmetrical carbocyanine dyes from 2 alkyl 4,5,6}?tetrahydrobenzothiazole quaternary salts, we react the quaternary saltswith esters of orthoacids, e. g. ethyl orthoiormate, ethyl orthoacetate,ethyl orthopropionate and ethyl orthobenzoate, in the presence ofpyridine.

To prepare unsymmetrical carbocyanine dyes from 2 alkyl 4,5,6,7tetrahydrobenzothiazole quaternary salts, we react the quaternary saltswith cyclammonium quaternary salts containing a p-arylaminovinyl groupin the alpha or gamma position, i. e. in one of the so-called reactivepositions, in the presence of an acid binding agent, e. g. pyridine.

To prepare dicarbocyanine dyes from Z-allzyl-4,5,6,7-tetrahydrobenzothiazcle quaternary salts, we react thequaternary salts with cyclammonium quaternary salts containing anw-arylaminobutadienyl group in the alpha or gamma position, in thepresence of an acid-binding agent, e. g. triethylamine dissolved inethyl or isopropyl alcohol.

The following examples will serve to demonstrate the manner of obtainingour new dyes.

These examples, however, are not intended to limit our invention:

EXAMPLE 1 1 ',3-diethyl -,5,6,7-tetmhydrothia-2 -cyanine iodide CzH5 Iing the mixture. Boiling was continued for about 20 minutes. At the endof this time, the reaction mixture was cooled and chilled to C. The dyeseparated from the chilled reaction mixture. The dye was filtered ozi,washed with acetone, then with water and finally with acetone, and thenallowed to dry in the air. A yield of 84% of dye was thus obtained. Thecrude dye was recrystallized from methyl alcohol (25 cc. per gram ofdye) and a 65% yield of pure dye was obtained. The pure dye was obtainedin the form of reddish-orange crystals which melted at 279 to 280 C.with decomposition.

EXAMPLE 2 3,3-diethyl4,5,6,7,4',5',6,7'-0ctahydr0thiacarbocyanine iodide3.09 g. (2 mol.) of 2-methyl-4,5,6,7-tetrahydrobenzothiazole ethiodideand 2.2 g. (3 mol.) of ethylorthoformate were mixed together in cc. ofdry pyridine. The resulting mixture was gently boiled, under reflux, forabout 2 hours. At the end of this time, the reaction mixture was cooledand diethyl ether was added to the reaction mixture to precipitate thedye. The precipitated dye was filtered off, washed with water and thenwith acetone, and finally allowed to dry in the air. The yield of crudedye was 12%. The crude dye was recrystallized from acetone (110 cc. pergram of dye) and an 8% yield of pure dye was obtained in the form ofgreenishbronze crystals melting at 216 to 217 C. with decomposition.

EXAMPLE 3 3,3-diethyl-9-meth1Z-4,5,6,7,4,5,6,7'metalwdrothzacarbocyanine iodide 3.09 g. (2 mol.) of2-methyl-4,5,6,7-tetrahydrobenzothiazole ethiodide and 2. g. (3 mol.) ofethyl orthoacetate were mixed together in 10 cc. of dry pyridine. Theresulting mixture was gently boiled, under reflux, for about 2%; hours.The reaction mixture was then cooled and diluted with 150 cc. of diethylether to precipitate the dye. The ethereal layer wa then decanted. Thesticky residue was stirred with another 159 cc. portion of diethyl etherand again the ethereal layer was decanted. The sticky residue wasdissolved in cc. of acetone and the resulting solution was diluted withdiethyl ether to precipitate the dye. The precipitated dye was filteredofi and washed with acetone and allowed to dry in the air. The yield ofcrude dye was 10%. After recrystallization from acetone (160 cc. pergram of dye) a yield of 6% of pure dye was obtained. The dye wasobtained in the form of dull dark green crystals, melting at 246 to 248C. with decomposition.

EXAMPLE 4 3,3',9-triethyZ-4,5,6,7,4',5',6',7-0ctahydrothiacarbocyanineiodide 7.06 g. (2 mol.) of 2-n1ethyl-4,5,6,7-tetrahydrobenzothiazoleetho-p-toluenesulfonate and 5.28 g. (3 mol.) of ethyl orthopropionatewere mixed together in 10 cc. of dry pyridine. The resulting mixture wasgently boiled, under reflux, for about 4 hours. At the end of this time,the hot reaction mixture was treated with a hot solution of potassiumiodide (5 g.) dissolved in water (50 cc.). The resulting mixture waschilled to 0 C. when the dye separated out. It was filtered off, washedwith water and finally stirred with boiling acetone (25 00.). Theacetone suspension was chilled to 0 C. and the dye filtered off andwashed with cold acetone and allowed to dry in the air. The yield ofcrude dye was 16% and after two recrystallizations from acetone cc. pergram of dye), a yield of pure dye of 7% was obtained. The dye wasobtained in th form of dark green crystals.

EXAMPLE 5 3,3'-diethyZ-4',5',6',7-tetrahydro-oxathidcarbocyam'ne iodide353' g. (1.1 mol.) of 2-methyl-4,5,6,7-tetrahy drobenzothiazoleetho-p-toluenesulfonate and 3.95 g. (1 mol.) of 2-(B-acetanilid0vinyl)-bcnzcxazole ethiodide were mixed together in 15 cc. of dry pyridine.The resulting mixture was gently boiled, under reflux, for about 10minutes. The reaction mixture was then cooled and diluted with cc. ofdiethyl ether. lhe ethereal layer was decanted and the residue wasstirred with 50 cc. of hot acetone. The resulting acetone suspension waschilled to 0 C. and the dye was filtered oil and washed with coldacetone. The dye was allowed to dry in the air. The yield of crude dyewas 45% and after two recrystallizations from methyl alcohol (45 cc. pergram of dye), a 26% yield of pure dye was obtained. The pure dye wasobtained in the form of dark purple crystals having a blue reflexmelting 247 to 248 C. with decomposition.

EXAMPLE 6 4.42 g. (1.3 mol.) of 2-methyl-4,5,6,7-tetrahydrobenzothiazolemetho-p-toluenesulfonate and 4.5 g. (1 mol.) of 2-(s-acetanilidovinyl)-benzothiazole ethiodide were mixed together in 15cc. of dry pyridine. The resulting mixture was gently boiled, underreflux, for about 10 minutes. The reaction mixture was then chilled andthe crystalline dye which separated was filtered off, washed withacetone and allowed to dry in the air. The yield of crude dye was 62%and after recrystallization from methyl alcohol (75 cc. per gram ofdye), a yield of pure dye of 42% was obtained. The pure dye was in theform of dark green needles having a blue reflex and melting at 273 to274 C. with decomposition.

EXAMPLE 7 Neocarbocyanine perchlorate from Z-mdthyl-4,5,6,7-tetrahyclrobenzothiazole 7.06 g. (3 mol.) of2-methyl-4,5,6,7-tetrahydrobenzothiazole etho-p-toluenesulfonate and4.44 g. (1 mol.) of ethyl orthoformate were mixed together in 10 cc. ofdry pyridine. The resulting mixture was gently boiled, under reflux, forabout 4 hours. The hot reaction mixture was then treated with a hotsolution of potassium iodide (5 g.) in water (50 cc.) and the resultingmixture was chilled at C. The dye which separated was filtered oh andwashed with water. The dye was then stirred with 25 cc. of hot acetone.The resulting suspension was chilled to 0 C. and the dye filtered oifand washed with cool acetone. The yield of crude dye-iodide was 32%, andafter two recrystallizations from 95% ethyl alcohol (25 cc. per gram ofdye) a yield of pure dye of 18% was obtained. The pure dye-iodide wasdissolved in hot methyl alcohol (20 cc.) and to the hot solution wasadded a hot solution of sodium perchlorate (1 g. in 2.0 cc. of water).The resulting solution was chilled to 0 C. and the dyeperchlorate wasfiltered 01f. It was recrystallized from 95% ethyl alcohol ('70 00. pergram of dye) and obtained as shiny green crystals, melting at 244 to 246C. with decomposition.

2-alkyl-4,5,6,7-tetrahydrobenzothiazoles can be prepared as described bySmith and Sapiro in Transactions of the Royal Society of South Africa,vol. 18, pages 229-235, 1929.

Quaternary salts of 2-alkyl-4,5,6,7-tetrahydrobenzothiazoles can beprepared as illustrated in the following examples:

EXAMPLE 8 Z-methyl-4,5,6,7-tetrahydrobenzothiaeole ethiodide 1.53 g. of2-methyl-4,5,6,7-tetrahydrobenzothiazole and 2.0 g. of ethyl iodide wereheated together, under reflux, for about 24 hours. The

solid reaction product consists essentially of the quaternary salt andcan be used without further purification.

EXAMPLE 9 2-methyl-4,5,6,7-tetrahydrobenzothiazo le 10etho-p-toluenesulfonate 3.06 g. of2-methyl-4,5,6,7-tetrahydrobenzothiazole and 4.0 g. ofethyl-p-toluenesulfonate were heated together at 100 C. for four days.The solid reaction product consists essentially of the quaternary saltand can be used without further purification. Themetho-p-toluenesulfonate can be similarly formed by using methyl insteadof ethyl-p-to1uenesulfonate.

To sensitize photographic silver halide emulsions with our new dyes, wedisperse the dyes in the emulsions. Our invention is particularlydirected to the customarily employed gelatinosilver-halide emulsions,such a the gelatinosilver-bromide, bromiodide, chloride andchlorobromide for example. The methods of incorporating dyes inemulsions are simple and well known to those skilled in the art. Inpracticing our invention, it is convenient to add the dyes fromsolutions in appropriate solvents. Methanol has proven satisfactory as asolvent for our new dyes. The dyes are advantageously incorporated inthe finished, washed emulsions and should be uniformly distributedthroughout tosecure best results.

The concentration of our new dyes in the emulsions can vary widely, e.g. from about 5 to about 100 mg. per liter of flowable emulsion. Theconcentration of the dye will vary according to the type oflight-sensitive material in the emulsion and according to the efiectsdesired. The suitable and most economical concentration for any givenemulsion will be apparent to those skilled in the art, upon making theordinary tests and observations customarily used in the art ofemulsion-making. To prepare a gelatino-silverhalide emulsion sensitizedwith one of our new dyes, the following procedure is satisfactory: Aquantity of the dye is dissolved in methyl alcohol, and a volume of thesolution (which may be diluted with water) containing from 5 to 100 mg.of dye is slowly added to about 1000 cc. of a gelatin-o-silver-halideemulsion with stirring. Stirring is continued until the dye is uniformlydispersed. With the more powerful of our new sensitizing dues, 10 to 20mg. of dye per 1000 cc. of emulsion sufiice to produce the maximumsensitizing effect with the ordinary gelatino-silyer-halide emulsions.The above statements are only illustrative and not to be understood aslimiting our invention in any sense, as it will be apparent that ourdyes can be incorporated by other methods in many of the photographicemulsions customarily employed in the art, such, for instance, as bybathing the plate or film upon which the emulsion is coated, in asolution of the dye in an appropriate solvent, although such a method isordinarily not to be preferred. The claims are intended to cover anycombination of these new dyes with a photo-graphic silver halideemulsion whereby the dyes exert a sensitizing effect on the emulsion.

The following table contains data which show the sensitizing range ofour new dyes on photographic silver halide emulsions:

Table Sensitivity Maximum Emulsion Dye (mg. per liter of emulsion)extends sensitivity M'u ll [it Gelatino-silver-bromiodide (about 40 g.of silver halide 1,3-cliethyl-4,5,6,7-tetrahydrothia-2-cyanine iodide.10 mg. 575 540 per liter of emulsion).

Do 3, 3-d1ethyl-4, 5, 6, 7, 4, 5 ,6, 7-octahydrothiacarbooyanine 645 610iodide. 10 m Do 3,3-diethyl-9-methyl 4,5.6,7,4,5,6,7-octahydrothiacarbo-615 580 cyanine iodide. 10 mg. D3,3,9-triethyl-4,5,6,7,4,5,6,7-0ctahydrothiacarbocyanine 615 580 iodide.10 mg. Do 3,3 diethyl 4,5,6,7 tctrahydro oxathiacarbocyanine '35 560iodide. mg. Do 3-ethyl-3-methyl4',5,6,7-tetrahydrothiacarbocyanine 640600 iodide. 10 mg. Do Neothiazolooarbocyanine perchlorate from2-methyl-4,5, 725 680 6,7-tetrahydrobenzothiazole. mg.

Photographic elements comprising our new dyes can be prepared in theusual manner by coating the emulsions on a. suitable support (e. g.glass, cellulose derivative film, resin film or photographic paper) tosuitable thickness and drying the coated emulsion.

What We claim as our invention and desire to be secured. by LettersPatent of the United States l. A dye selected from the groupcharacterized by the following general formula:

wherein R and R represent alkyl groups, R" represents a substituentselected from the group consisting of hydrogen and alkyl groups and Xrepresents an acid radical.

2. 3,3'-diethy1-4,5,6,7,4',5,6','7'-- octahydrothiacarbocyanine iodide.

3. 3,3 diethy1-9-methy1-4,5,6,'7,4',5,6',7-octahydrothiacarbocyanineiodide.

4. 3,3',9- triethyl -4,5,6,7,4=',5',6',7' octahydrothiacarbocyanineiodide.

LESLIE G, S. BROOKER. FRANK L. WHITE.

